The wheels and bearings Isolate the motion of the airplane from the motion of the tread mill.
So the treadmill has no "drag" on the airplane at all.
This is clearly demonstrated by the video experiment by the elementary school boy and his father.
Despite the fact that the treadmill was easily running ten times as fast as that toy plane could travel on the ground, the propeller was able to pull the vehicle to the front of the treadmill.
The wheels isolated the the motion of the treadmill from the thrust of the propeller.
If this experiment were to be recreated with a longer treadmill the plane would eventually get up enough speed to take off.
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The roller blades and rope are a good example also.[8D]